1. Field of the Invention
The present invention relates generally to calender units that use crush rollers to crush powders and other superfluous materials on the surface of printing media and more specifically to a calender unit that combines crush rollers, brush rollers and a vacuum cleaning system for use in a screen process printing machine.
2. Prior Art
Calender rollers for cleaning or smoothing fabrics, print stock or other material are well known in the prior art. By way of example:
U.S. Pat. No. 3,991,669 to Cumbers is directed to a calender press wherein a complaint roll is in contact with a rigid roll. The calender press of this reference includes a rigid roll which is in contact along its length with a hollow, thin-walled compliant roll. The compliant roll deforms elastically due to its thin wall and hollow construction.
U.S. Pat. No. 4,498,383 to Pav et al is directed to a calender system wherein one of a pair of rolls has an external surface formed of a deformable, elastic substance. The calendar includes a rigid roll which contacts a roll comprising an elongated hollow cylindrical shell surrounded by an elastic liner. The liner may consist of any of a variety of materials which exhibit visco-elastic characteristics, like that of cast or extruded synthetic plastic, or natural or synthetic rubber.
U.S. Pat. No. 2,730,770 to Higginbotham et al is directed to clearing rolls for maintaining calender rolls in a clean condition. The clearing rolls are positioned so as to contact the pressure rolls of the illustrated machine. The clearing rolls are formed by a roll body of elastic material such as expanded rubber, and covered by a flock covering.
U.S. Pat. No. 1,911,930 to Schultze is directed to a cleaning device for use on machines with cylindrical rolls. The cleaning brush is moved over the stretching cylinders of a textile stretching machine. The machine also includes a cylindrical brush which cleans both the cleaning cylinder and the upper cylinders.
U.S. Pat. No. 4,510,864 to Klemm is directed to a screen printing machine having a drying path. The screen printer of this reference makes use of heated rollers to dry the ink, as opposed to using litho printing powder.
Screen process printing machines are also well known in the art. Typically, screen process printing machines serially feeds paper stock onto a roller where ink is applied to the stock through a screen of predetermined layout to deposit the ink in desired locations. When the stock is clean, that is the surface is free of any extraneous materials, the ink can be easily deposited in desired locations without any difficulty. However, there has recently been developed a relatively new use for screen process printing machines in which paper stock having lithographic powder on its surface is fed onto the roller. This new use is called a liquid lamination process and is employed for applying glossy film finishes or coatings to print stock. The screen process printing machine applies the chemical coating which is then cured, usually by the application of ultraviolet light to the coated stock. Unfortunately, the presence of such powders on the printing stock can detrimentally effect the coating deposition process particularly when such powders have agglomerated on the printed surface of the stock. As a result, the coating may be deposited over the agglomerations of lithographic powder thereby preventing the deposition from producing a smooth coated surface. Therefore, it is important to provide a means for allowing the use of lithographic powders on paper stock fed to a screen process cylinder while avoiding any such powder agglomerations on the stock before it reaches the coating deposition screen. Unfortunately, no prior art screen process printing machine known to the applicants herein has integrated a calender or crush roller unit into a screen process printing machine. Accordingly, it has been necessary to either carefully wipe clean every sheet of paper stock before it is fed to a screen process printing machine or attempt to minimize the application of lithographic powder to reduce interference with the coating process. Furthermore, merely adapting prior art calender roll assemblies of the known prior art to existing screen process printing machines would be extremely difficult, if not impossible without avoiding interference with the screen process printing machine feeding mechanism and without substantially increasing the maintenance requirements for frequent and periodic cleaning of the crush roller unit in order to keep the screen process printing machine working efficiently and effectively.
There has therefore been a long felt need for an integrated calender and brush roller unit and screen process printing machine which enables the use of lithographic powders on the printing stock while assuring that no powder agglomerations will be produced and which would otherwise interfere with the screen process coating performance. Furthermore, there has been a long felt need for such an integrated unit which does not substantially increase the maintenance requirements for the screen process printing machine as previously outlined.